발 and 팔 can sound similar to new learners but of course they are not the same. One needs to listen very carefully to discern the difference. 팔 has the ㅍ sound which is similar to the English P (pal). The small difference is that I think ㅍ is more guttural, with the back of the mouth and the throat area vibrating more than with the English P sound, which is more exclusively made in the front of the mouth and therefore sounds lighter. To pronounce ㅂ, the main difference from ㅍ is that it doesn't have the sharp puffing (aspiration) of the air and therefore is duller. In other aspects it is quite close to ㅍ - it should not be too much like English B. The sound is dull and heavy with the throat area vibrating more. Unfortunately the difference is not that big so you'll need to practice picking up the difference. One way to practice is using Google Translate. Go to "translate.google.com" and enter "발은 팔은" for example in the left hand side box and set the language to Korean. If you click on the speaker icon you'll hear the pronunciation. I think its pronunciation is not bad for this particular case. But note the last syllable seems to be distorted, so don't put what you want to hear at the end. Also the funny thing is that if I enter "발도 팔도" instead, the 팔 sound now becomes like an unclear 발 for some reason. So don't trust it 100%. But at least for "발은 팔은" I think I hear the difference clear enough.

Haha. I have this same problem. I think it's tough for English speakers to hear the difference. "팔" is pronounced with an aspirated "p" sound. I think it should sound like the "p" in "palace". I think "발" has a sound somewhere between "b" and "p" in English. Try saying "balee" and "palee" with a sound that could be either one. Note that the "ㄹ" has a sound between "R" and "L". But that's a problem for another day. ㅋㅋ